This Center is designed to define the contributions of the vestibular system to the control of balance, posture and locomotion through an integrated series of ground-based studies, three examining the vestibular-neck (vestibulocollic) reflex and three the vestibulospinal control of standing posture. One theme of the Center is to exploit the synergy between these two set of studies to produce the first complete whole body model of posture. Any model that is to lead to an adequate understanding of the postural system must incorporate and interrelate mechanisms that stabilize the head in space, the trunk with respect to the head and body center of mass with respect to gravity. Heretofore no investigator or group has had the broad array of skills and insights to attempt such a model or to undertake the interactive experiments needed to obtain the data upon which it must be based. This Center will provide the skills and resources to accomplish this important task which the field has been awaiting for a long time. The second theme of the Center is to focus upon the vestibular otolith organs and the sensory motor responses that occur when they are stimulated by gravitational forces or linear motions. Projects 1, 2 and 6 will bring on line new devices designed specifically to study otolith systems. Modelers involved in Projects 1, 2, 4 and 5 will simulate and model for the first time the role of neural pathways originating in otolith organs in stabilization of the head and body and in locomotion. Recordings proposed in Project 2 will yield the first 3-dimensional analysis of otolith signals at the level of vestibulospinal neurons. Collectively these activities will greatly increase our knowledge of otolith systems, which are of special importance for understanding how the neuro-vestibular system senses and adapts to the alteration in gravity that occurs when a space craft enters orbit and returns to earth with attendant problems of disorientation and dysequilibrium. A third theme of the Center is its extensive use of computational modeling. Projects 1 and 4 share the use of an elegant new biomechanical model that allows one to construct accurate models of musculo-skeletal systems, whose kinetic properties can then be simulated under a wide variety of conditions. Projects 1 and 5 employ non-linear systems models to simulate how central nervous system control of head or body position interacts with body biomechanics. Project 2 uses new neural network modeling approaches to analyze the function of circuits that incorporate the known connectivity of vestibulocollic pathways. Our goal is for these modeling efforts to coalesce into a multi-level model that both simulates postural stabilizing responses observed by us and others and suggests further experiments that will more effectively illumine the functions of the vestibulospinal system. The Center will also have a training component designed to give pre- and postdoctoral trainees unique opportunities to work with outstanding vestibular physiologists and modelers and to participate in work on several Center projects, thus contributing to the cross-fertilization taking place within the Center.